Ti6Al4V is widely used in industry due to its outstanding mechanical properties. However, the severe abrasion and high temperature at tool/chip and tool/workpiece interfaces cause various types of tool wear in machining Ti6Al4V. To ensure high machining efficiency and high quality of machined surface, cooling fluid is often used to reduce the cutting temperature and friction. In this paper, the cooling and lubricating effects of coolant with graphene oxide nanosheet suspension were investigated experimentally and theoretically. Cutting experiments were conducted to compare the performance of conventional coolant with that of the coolant with graphene oxide nanosheets of different weight percentages (0.1% and 0.5%). Cutting force and temperature on the rake face were measured in each cutting pass. A theoretical model based on computational fluid dynamics (CFD) was developed to investigate the temperature distribution and cooling efficiency quantitatively. Friction force and coefficient of friction at tool/chip interface and tool/workpiece interface were calculated to analyse the lubrication effects of different types of coolant. The results showed that the performance of cooling and lubrication of the coolant became better with the addition of graphene oxide nanosheets. Results from the analysis of flank wear and crater wear and the morphological characteristics proved that there was a significant further reduction in cutting temperature and friction force when coolant with graphene oxide nanosheets was used.